In the past, the most typical practice in tape recorders was to mount the transducer heads in relatively fixed position in which the tape-to-head position was more or less permanently established. Sometimes the heads were not moved at all from such established position during operation, and at other times they were moved only toward and away from the tape, to facilitate tape changes, etc.; in either such case, however, when transducing was to occur the tape and the head always engaged one another in essentially the same position and at the same location relative to the width of the tape. When multi-track operation was desired, the most typical approach was to invert the tape, employing transducer positioning which accessed only one-half (or other such portion) of the tape at any particular time and which covered the other half, or portion, as a result of, in effect, changing the transport position of the tape.
In most recent times, with the advance of technology and the increasingly demanding performance objectives and capabilities presented, particularly in data storage applications, it has become increasingly desirable to provide for multiple-track tape recording systems, with narrow and closely spaced recording tracks.
These events have brought about the need for commensurately precise and reliable multiple-track positioning apparatus for tape heads, since of course each different track must be accessible to the transducer at any desired time, demanding the capability of at least a number of precise, incremental position shifts at desired times while maintaining desired head-to-tape azimuth angles, tape wrap or tape-head contact, etc., and in fact requiring other complexities as well, including for example the ability to move the transducer head orthogonally away from the plane of the tape at desired times, particularly for such operations as tape changes and the like. More particularly still, however, is the requirement for a positioner which not only satisfies all of the foregoing requirements but, in addition, provides for the capability of continuous position changes of randomly changing magnitude laterally with respect to the tape, whereby any of the multiple recording tracks on the tape may in effect be followed, i.e., tracked, by servo control during tape transport, to accommodate a wide variety of possible irregular tape motion relative to the transducer in addition to, and apart from, the mere lengthwise transport of the recording tracks by which transitions are recorded or reproduced, resulting from the inability, as a practical matter, to guide a tape in precisely the same position relative to the head at all times along the length of the tape each time transport occurs, while also providing for interchangeability in tape media.